Power-Beaming Technology for Laser Propulsion

This introduction to beamed-energy propulsion addresses some of the background issues and technology relating to such items as laser power sources, mirrors, desired wavelength, pointing, and tracking. The laser thruster configurations are surveyed by other papers in the chapter. The laser energy absorption schemes suggested in the laser propulsion literature include: inverse bremsstrahlung, particulate and molecular seeding, and heatexchanger mechanisms. Both continuously-operating (CW) and repetitively-pulsed (RP) thrusters have been tested. Studies of candidate molecular absorbers indicate a clear preference for specific laser wavelengths. Present understanding does not permit the prediction of which thruster concept and associated wavelength/waveform will lead to superior performance with future full-scale engines. Furthermore, a given thruster concept may be ideal for some missions, but inferior for others. Also, orbit-raising missions with attendant ranges of 10^ km or more will dictate the use of very short wavelengths (e.g., from 0.35 to 2.5 ym), which may, to a large extent, predetermine the choice of thruster concept. Regardless of the long-term outcome